Nonwoven fabric and associated composite and methods of making

ABSTRACT

A nonwoven fabric useful for forming composite panels includes specific amounts of reinforcing fibers, a polyimide, and a block polyestercarbonate-polysiloxane. The nonwoven fabric has a density of 0.03 to 0.2 gram/centimeter 3 , an areal density of 100 to 400 gram/meter 2 , and a tensile modulus of 50 to 1000 megapascals. Also described are a method of forming the nonwoven fabric, a composite formed from the nonwoven fabric, and a method of forming the composite.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and U.S. Patent Application No.62/671,429 filed 15 May 2018, and European Patent Application No.18197230.8 filed 27 Sep. 2018, both of which are incorporated byreference herein in their entirety.

BACKGROUND OF THE INVENTION

Fiber-reinforced thermoplastics are increasingly used in the fabricationof interior parts for vehicles including aircraft, ships, and trains.For example, U.S. Patent Application Publication No. US 2012/0065283 A1of Adjei et al. describes a nonwoven fabric prepared from reinforcingfibers, polyimide fibers, and polymeric binder fibers. Multiple layersof the nonwoven fabric are combined under elevated temperature andpressure to form a composite sheet that is optionally combined with adecorative film to form the vehicular interior part. Such parts exhibitadvantageous properties including low weight, high flame retardancy, andlow smoke generation. However, there is a desire for nonwoven fabricsthat facilitate handling, as well as composite sheets that exhibitimproved surface uniformity.

BRIEF SUMMARY OF EMBODIMENTS OF THE INVENTION

One embodiment is a nonwoven fabric, comprising, based on the weight ofthe nonwoven fabric: 25 to 55 weight percent of reinforcing fibers, 35to 65 weight percent of a polyimide, and 5 to 20 weight percent of ablock polyestercarbonate-polysiloxane; wherein the blockpolyestercarbonate-polysiloxane comprises a polyester block comprisingresorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of IV groups arearomatic divalent groups, and a polysiloxane block comprisingdimethylsiloxane units; wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5to 35 mole percent of carbonate units wherein R¹ is 1,3-phenylene, and 5to 35 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weightpercent dimethylsiloxane units; wherein the nonwoven fabric has adensity of 0.03 to 0.2 gram/centimeter³, and an areal density of 100 to400 gram/meter²; and wherein the nonwoven fabric has a tensile modulusof 50 to 1000 megapascals, determined according to ASTM D638-14 at atemperature of 23° C. and using a test speed of 50 millimeters/minute.

Another embodiment is a method of forming a nonwoven fabric, the methodcomprising: forming an aqueous suspension layer comprising water, 25 to55 weight percent of reinforcing fibers, 35 to 65 weight percent ofpolyimide fibers, and 5 to 20 weight percent of binder fibers comprisinga block polyestercarbonate-polysiloxane, wherein weight percent valuesare based on the total weight of reinforcing fibers, polyimide fibers,and binder fibers; at least partially removing water from the aqueoussuspension layer to form a fiber layer; and exposing the fiber layer toa temperature of 250 to 320° C., thereby melting the binder fibers, atleast partially melting the polyimide fibers, and forming a nonwovenfabric; wherein the block polyestercarbonate-polysiloxane comprises apolyester block comprising resorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R¹ groups arearomatic divalent groups, and a polysiloxane block comprisingdimethylsiloxane units; wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5to 35 mole percent of carbonate units wherein R¹ is 1,3-phenylene, and 5to 35 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weightpercent dimethylsiloxane units.

Another embodiment is a composite, comprising, based on the weight ofthe composite: 25 to 55 weight percent of reinforcing fibers, 35 to 65weight percent of a polyimide, and 5 to 20 weight percent of a blockpolyestercarbonate-polysiloxane; wherein the blockpolyestercarbonate-polysiloxane comprises a polyester block comprisingresorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R¹ groups arearomatic divalent groups, and a polysiloxane block comprisingdimethylsiloxane units; wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5to 35 mole percent of carbonate units wherein R¹ is 1,3-phenylene, and 5to 35 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weightpercent dimethylsiloxane units; and wherein the composite has a densityof 0.92 to 1.38 gram/centimeter³, and an areal density of 100 to 3000gram/meter².

Another embodiment is a method of forming a multilayer composite, themethod comprising: exposing at least two layers of the nonwoven fabricin any of its variations to a temperature of 250 to 400° C. and apressure of 300 to 1,500 kilopascals for a time of 60 to 600 seconds toyield a multilayer composite.

These and other embodiments are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a melt spinning apparatus.

FIG. 2 is a schematic illustration of a papermaking apparatus.

FIG. 3A is an image of a roll of 325 gram/meter² non-consolidatednonwoven fabric; FIG. 3B is an image of a roll of 165 gram/meter²pre-consolidated nonwoven fabric.

FIG. 4A is an optical micrograph of a cross-section of 325 gram/meter²non-consolidated nonwoven fabric; FIG. 4B is an optical micrograph of across-section of 165 gram/meter² pre-consolidated nonwoven fabric.

FIG. 5A is a surface profile derived from an optical micrograph of 325gram/meter² non-consolidated nonwoven fabric; FIG. 5B is a surfaceprofile derived from an optical micrograph of 165 gram/meter²pre-consolidated nonwoven fabric.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have determined that nonwoven fabrics can beformulated to exhibit increased stiffness that facilitates handling ofthe fabrics as they are used to prepare composites. The formulation ofthe present nonwoven fabric also leads to better retention ofreinforcing fibers during handling of the nonwoven fabric. And use ofthe present nonwoven fabric also improves the surface uniformity ofcomposites prepared from it.

Thus, one embodiment is a nonwoven fabric, comprising, based on theweight of the nonwoven fabric: 25 to 55 weight percent of reinforcingfibers, 35 to 65 weight percent of a polyimide, and 5 to 20 weightpercent of a block polyestercarbonate-polysiloxane; wherein the blockpolyestercarbonate-polysiloxane comprises a polyester block comprisingresorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R¹ groups arearomatic divalent groups, and a polysiloxane block comprisingdimethylsiloxane units; wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5to 35 mole percent of carbonate units wherein R¹ is 1,3-phenylene, and 5to 35 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weightpercent dimethylsiloxane units; wherein the nonwoven fabric has adensity of 0.03 to 0.2 gram/centimeter³, and an areal density of 100 to400 gram/meter²; and wherein the nonwoven fabric has a tensile modulusof 50 to 1000 megapascals, determined according to ASTM D638-14 at atemperature of 23° C. and using a test speed of 50 millimeters/minute.

The nonwoven fabric includes reinforcing fibers. Reinforcing fibersinclude metal fibers, metallized inorganic fibers, metallized syntheticfibers, glass fibers, graphite fibers, carbon fibers, ceramic fibers,mineral fibers, basalt fibers, polymer fibers having a melting or glasstransition temperature at least 150° C. higher than the glass transitiontemperature of polyimide, and combinations thereof. In some embodiments,the reinforcing fibers comprise glass fibers. As used herein, the term“fibers” refers specifically to fibers having a diameter of 5 to 125micrometers, and a length of 5 to 75 millimeters. Within the range of 5to 125 micrometers, the diameter can be 10 to 100 micrometers, or 10 to50 micrometers, or 10 to 25 micrometers. Within the range of 5 to 75millimeters, the fiber length can be 6 to 50 millimeters, or 7 to 40millimeters, or 10 to 30 millimeters.

The nonwoven fabric includes the reinforcing fibers in an amount of 25to 55 weight percent, based on the weight of the nonwoven fabric. Withinthis range, the amount of reinforcing fibers can be 30 to 50 weightpercent.

In addition to the reinforcing fibers, the nonwoven fabric comprises apolyimide. A polyimide is a polymer comprising a plurality of repeatingunits having the structure

wherein U is independently at each occurrence a tetravalent linkerselected from the group consisting of substituted or unsubstituted,saturated, unsaturated, or aromatic monocyclic and polycyclic groupshaving 5 to 50 carbon atoms, substituted or unsubstituted alkyl groupshaving 1 to 30 carbon atoms, and substituted or unsubstituted alkenylgroups having 2 to 30 carbon atoms; and R² is independently at eachoccurrence a divalent group selected from the group consisting ofsubstituted or unsubstituted divalent aromatic hydrocarbon moietieshaving 6 to 20 carbons, straight or branched chain alkylene moietieshaving 2 to 20 carbons, cycloalkylene moieties having 3 to 20 carbonatom, and divalent moieties of the general formula

wherein Q is selected from the group consisting of —O—, —S—, —C(O)—,—S(O)₂—, —S(O)—, and —C_(y)H_(2y)— where y is 1 to 20. The number ofrepeating units in the polyimide can be, for example, 10 to 1,000,specifically 10 to 500.

Exemplary tetravalent linkers, U, include tetravalent aromatic radicalsof the formula

wherein W is a divalent moiety such as —O—, —S—, —C(O)—, —SO₂—, —SO—,—C_(y)H_(2y)— (y being an integer of 1 to 20), and halogenatedderivatives thereof, including perfluoroalkylene groups, or a group ofthe Formula —O—Z—O— wherein the divalent bonds of the —O— or the —O—Z—O—group are in the 3,3′, 3,4′, 4,3′, or the 4,4′ positions, and wherein Zincludes divalent moieties of the formula

wherein Q is divalent moiety that can be —O—, —S—, —C(O)—, —SO₂—, —SO—,—C_(y)H_(2y)— wherein y is 1 to 8, or —C_(p)H_(q)F_(r)— where p is from1 to 8 and q is 0 to 15 and r is 1 to 16 and q+r=2p. In some embodimentsthe tetravalent linker U is free of halogens.

In some embodiments, the polyimide comprises a polyetherimide.Polyetherimides comprise repeating units of formula

wherein T is —O— or a group of the Formula —O—Z—O— wherein the divalentbonds of the —O— or the —O—Z—O— group are in the 3,3′, 3,4′, 4,3′, orthe 4,4′ positions of the phthalimide groups, and wherein Z and R² aredefined as described above. In some embodiments, each occurrence of R²is independently p-phenylene or m-phenylene, and T is a divalent moietyof the formula

Included among the many methods of making polyimides, includingpolyetherimides, are those disclosed in U.S. Pat. No. 3,847,867 to Heathet al., U.S. Pat. No. 3,850,885 to Takekoshi et al., U.S. Pat. Nos.3,852,242 and 3,855,178 to White, U.S. Pat. No. 3,983,093 to Williams etal., and U.S. Pat. No. 4,443,591 to Schmidt et al.

In some embodiments, the polyimide comprises a polyetherimide comprising10 to 1000 repeating units having the structure

wherein T is —O— or a group of the formula —O—Z—O— wherein the divalentbonds of the —O— or the —O—Z—O— group are in the 3,3′, 3,4′, 4,3′, orthe 4,4′ positions, and wherein Z is selected from the group consistingof

wherein Q is divalent moiety selected from the group consisting of —O—,—S—, —C(O)—, —SO₂—, —SO—, —C_(y)H_(2y)— where y is 1 to 8, and—C_(p)H_(q)E_(r)- where p is from 1 to 8, q is 0 to 15, r is 1 to 16,and q+r=2p; and R² is defined as described above.

In some embodiments, R² is independently at each occurrencemeta-phenylene or para-phenylene, and U has the structure

The repeating units of the polyimide are formed by the reaction of adianhydride and a diamine. Dianhydrides useful for forming the repeatingunits include those having the formula

wherein U is as defined above. As mentioned above the term dianhydridesincludes chemical equivalents of dianhydrides. In some embodiments, thedianhydride comprises an aromatic bis(ether anhydride). Examples ofspecific aromatic bis(ether anhydride)s are disclosed, for example, inU.S. Pat. No. 3,972,902 to Heath et al. and U.S. Pat. No. 4,455,410 toGiles. Illustrative examples of aromatic bis(ether anhydride)s include2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride,4,4′-bis(3,4-dicarboxyphenoxy)diphenyl ether dianhydride,4,4′-bis(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride,4,4′-bis(3,4-dicarboxyphenoxy)benzophenone dianhydride,4,4′-bis(3,4-dicarboxyphenoxy)diphenyl sulfone dianhydride,2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride,4,4′-bis(2,3-dicarboxyphenoxy)diphenyl ether dianhydride,4,4′-bis(2,3-dicarboxyphenoxy)diphenyl sulfide dianhydride,4,4′-bis(2,3-dicarboxyphenoxy)benzophenone dianhydride,4,4′-bis(2,3-dicarboxyphenoxy)diphenyl sulfone dianhydride,4-(2,3-dicarboxyphenoxy)-4′-(3,4-dicarboxyphenoxy)diphenyl-2,2-propanedianhydride, 4-(2,3-dicarboxyphenoxy)-4′-(3,4-dicarboxyphenoxy)diphenylether dianhydride,4-(2,3-dicarboxyphenoxy)-4′-(3,4-dicarboxyphenoxy)diphenyl sulfidedianhydride,4-(2,3-dicarboxyphenoxy)-4′-(3,4-dicarboxyphenoxy)benzophenonedianhydride, 4-(2,3-dicarboxyphenoxy)-4′-(3,4-dicarboxyphenoxy)diphenylsulfone dianhydride, and mixtures thereof.

Diamines useful for forming the repeating units of the polyimide includethose having the formula

H₂N—R²—NH₂

wherein R² is as defined above. Examples of specific organic diaminesare disclosed, for example, in U.S. Pat. No. 3,972,902 to Heath et al.and U.S. Pat. No. 4,455,410 to Giles. Exemplary diamines includeethylenediamine, propylenediamine, trimethylenediamine,diethylenetriamine, triethylenetertramine, hexamethylenediamine,heptamethylenediamine, octamethylenediamine, nonamethylenediamine,decamethylenediamine, 1,12-dodecanediamine, 1,18-octadecanediamine,3-methylheptamethylenediamine, 4,4-dimethylheptamethylenediamine,4-methylnonamethylenediamine, 5-methylnonamethylenediamine,2,5-dimethylhexamethylenediamine, 2,5-dimethylheptamethylenediamine,2,2-dimethylpropylenediamine, N-methyl-bis (3-aminopropyl) amine,3-methoxyhexamethylenediamine, 1,2-bis(3-aminopropoxy) ethane,bis(3-aminopropyl) sulfide, 1,4-cyclohexanediamine,bis-(4-aminocyclohexyl) methane, m-phenylenediamine, p-phenylenediamine,2,4-diaminotoluene, 2,6-diaminotoluene, m-xylylenediamine,p-xylylenediamine, 2-methyl-4,6-diethyl-1,3-phenylenediamine,5-methyl-4,6-diethyl-1,3-phenylenediamine, benzidine,3,3′-dimethylbenzidine, 3,3′-dimethoxybenzidine, 1,5-diaminonaphthalene,bis(4-aminophenyl) methane, bis(2-chloro-4-amino-3, 5-diethylphenyl)methane, bis(4-aminophenyl) propane, 2,4-bis(p-amino-t-butyl) toluene,bis(p-amino-t-butylphenyl) ether, bis(p-methyl-o-aminophenyl) benzene,bis(p-methyl-o-aminopentyl) benzene, 1, 3-diamino-4-isopropylbenzene,bis(4-aminophenyl) sulfide, bis (4-aminophenyl) sulfone,bis(4-aminophenyl) ether, 1,3-bis(3-aminopropyl) tetramethyldisiloxane,and mixtures thereof. In some embodiments, the diamine is an aromaticdiamine, more specifically, m-phenylenediamine, p-phenylenediamine,sulfonyl dianiline, or a mixture thereof.

In general, polyimide-forming reactions can be carried out employingvarious solvents, e.g., o-dichlorobenzene, m-cresol/toluene, and thelike, to effect a reaction between the dianhydride and the diamine, attemperatures of 100° C. to 250° C. Alternatively, the polyimide blockcan be prepared by melt polymerization or interfacial polymerization,e.g., melt polymerization of an aromatic bis(anhydride) and a diamine byheating a mixture of the starting materials to elevated temperatureswith concurrent stirring. Generally, melt polymerizations employtemperatures of 200° C. to 400° C.

A chain-terminating agent can be employed to control the molecularweight of the polyimide. Monofunctional amines such as aniline, ormonofunctional anhydrides such as phthalic anhydride can be employed.

In some embodiments, the polyimide has a melt index of 0.1 to 10 gramsper minute, determined according to ASTM D 1238-04 at 350° C., using a6.6 kilogram (kg) load. In some embodiments, the polyetherimide resinhas a weight average molecular weight of 10,000 to 150,000 grams permole, as determined by gel permeation chromatography using polystyrenestandards. In some embodiments, the polyetherimide has a weight averagemolecular weight of 20,000 to 60,000. In some embodiments, the polyimidehas an intrinsic viscosity greater than or equal to 0.2 deciliter pergram, specifically 0.35 to 0.7 deciliter per gram, measured by Ubbelohdeviscometer in m-cresol at 25° C.

The nonwoven fabric includes the polyimide in an amount of 35 to 65weight percent, based on the weight of the nonwoven fabric. Within thisrange, the amount of polyimide can be 40 to 60 weight percent.

In addition to the reinforcing fibers and the polyimide, the nonwovenfabric comprises a block polyestercarbonate-polysiloxane. A blockpolyestercarbonate-polysiloxane is a copolymer comprising at least onepolyester block, at least one polycarbonate block, and at least onepolysiloxane block. Specifically, the at least one polyester blockcomprises resorcinol ester units, each resorcinol ester unit having thestructure

the at least one polycarbonate block comprises carbonate units, eachcarbonate unit having the structure

wherein at least 60 percent of the total number of R¹ groups arearomatic divalent groups, and the at least one polysiloxane blockcomprises dimethylsiloxane units.

In some embodiments, the aromatic divalent groups are C₆-C₂₄ aromaticdivalent groups. When not all R¹ groups are aromatic, the remainder areC₂-C₂₄ aliphatic divalent groups. In some embodiments, each R¹ is aradical of the formula

wherein each of A¹ and A² is independently a monocyclic divalent arylradical, and Y¹ is a bridging radical having one or two atoms thatseparate A¹ from A². Examples of A¹ and A² include 1,3-phenylene and1,4-phenylene, each optionally substituted with one, two, or three C₁-C₆alkyl groups. The bridging radical Y¹ can be a C₁-C₁₂ (divalent)hydrocarbylene group. As used herein, the term “hydrocarbyl”, whetherused by itself, or as a prefix, suffix, or fragment of another term,refers to a residue that contains only carbon and hydrogen unless it isspecifically identified as “substituted hydrocarbyl”. The hydrocarbylresidue can be aliphatic or aromatic, straight-chain, cyclic, branched,saturated, or unsaturated. It can also contain combinations ofaliphatic, aromatic, straight chain, cyclic, bicyclic, branched,saturated, and unsaturated hydrocarbon moieties. When the hydrocarbylresidue is described as substituted, it can contain heteroatoms inaddition to carbon and hydrogen. In some embodiments, one atom separatesA¹ from A². Illustrative examples of Y¹ radicals are —O—, —S—, —S(O)—,—S(O)₂—, —C(O)—, methylene (—CH₂—; also known as methylidene),ethylidene (—CH(CH₃)—), isopropylidene (—C(CH₃)₂—), neopentylidene,cyclohexylidene, cyclopentadecylidene, cyclododecylidene,adamantylidene, cyclohexylidene methylene, cyclohexylmethylene, and2-[2.2.1]-bicycloheptylidene.

In some embodiments, the resorcinol ester units comprise resorcinolisophthalate/terephthalate units, and the carbonate units compriseresorcinol carbonate units and bisphenol A carbonate units.

The block polyestercarbonate-polysiloxane comprises, based on totalmoles of carbonate and ester units, 30 to 90 mole percent of theresorcinol ester units, 5 to 35 mole percent of carbonate units whereinR¹ is 1,3-phenylene (i.e., the carbonate units are resorcinol carbonateunits), and 5 to 35 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, which has the chemical structure

(i.e., the carbonate units are bisphenol A carbonate units). Within therange of 30 to 90 mole percent, the amount of resorcinol ester units canbe 50 to 90 mole percent, or 70 to 90 mole percent. Within the range of5 to 35 mole percent, the amount of resorcinol carbonate units can be 5to 25 mole percent, or 5 to 15 mole percent. Within the range of 5 to 35mole percent, the amount of bisphenol A carbonate units can be 5 to 25mole percent, or 5 to 15 mole percent. The blockpolyestercarbonate-polysiloxane further comprises, based on the weightof the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percentdimethylsiloxane units. Within this range, the amount ofdimethylsiloxane units can be 0.4 to 2 weight percent, or 0.5 to 2weight percent.

In a very specific embodiment, the block polyestercarbonate-polysiloxanecomprises, based on total moles of carbonate and ester units, 70 to 90mole percent of resorcinol isophthalate/terephthalate units, 5 to 15mole percent of resorcinol carbonate units, and 5 to 15 mole percent ofbisphenol A carbonate units, and further comprises dimethylsiloxaneunits in an amount, based on the total weight of the blockpolyestercarbonate-polysiloxane, of 0.5 to 2 weight percent.

There is no particular limit on the structure of end groups on the blockpolyestercarbonate-polysiloxane. An end-capping agent (also referred toas a chain stopping agent or chain terminating agent) can be includedduring polymerization to provide end groups. Examples of end-cappingagents include monocyclic phenols such as phenol, p-cyanophenol, andC₁-C₂₂ alkyl-substituted phenols such as p-cumylphenol, resorcinolmonobenzoate, and p-tertiary-butyl phenol; monoethers of diphenols, suchas p-methoxyphenol; monoesters of diphenols such as resorcinolmonobenzoate; functionalized chlorides of aliphatic monocarboxylic acidssuch as acryloyl chloride and methacryoyl chloride; andmono-chloroformates such as phenyl chloroformate, alkyl-substitutedphenyl chloroformates, p-cumyl phenyl chloroformate, and toluenechloroformate. Combinations of different end groups can be used. In someembodiments, the block polyestercarbonate-polysiloxane has a weightaverage molecular weight of 15,000 to 55,000 grams/mole, as determinedby gel permeation chromatography using polycarbonate standards. Withinthis range, the weight average molecular weight can be 18,000 to 50,000grams/mole.

Methods for the preparation of block polyestercarbonate-polysiloxanesare known and described, for example, in U.S. Pat. No. 7,790,292 B2 toColborn et al.

The nonwoven fabric comprises the block polyestercarbonate-polysiloxanein an amount of 5 to 20 weight percent, based on the weight of thenonwoven fabric. Within this range, the amount of blockpolyestercarbonate-polysiloxane can be 5 to 15 weight percent.

The nonwoven fabric can, optionally, further comprise an organophosphateester flame retardant. Exemplary organophosphate ester flame retardantsinclude phosphate esters comprising phenyl groups, substituted phenylgroups, or a combination of phenyl groups and substituted phenyl groups,bis-aryl phosphate esters based upon resorcinol such as, for example,resorcinol bis(diphenyl phosphate), as well as those based uponbisphenols such as, for example, bisphenol A bis(diphenyl phosphate). Insome embodiments, the organophosphate ester is selected fromtris(alkylphenyl) phosphates (for example, CAS Reg. No. 89492-23-9 orCAS Reg. No. 78-33-1), resorcinol bis(diphenyl phosphate) (CAS Reg. No.57583-54-7), bisphenol A bis(diphenyl phosphate) (CAS Reg. No.181028-79-5), triphenyl phosphate (CAS Reg. No. 115-86-6),tris(isopropylphenyl) phosphates (for example, CAS Reg. No. 68937-41-7),t-butylphenyl diphenyl phosphates (CAS Reg. No. 56803-37-3),bis(t-butylphenyl) phenyl phosphates (CAS Reg. No. 65652-41-7),tris(t-butylphenyl) phosphates (CAS Reg. No. 78-33-1), and combinationsthereof. In some embodiments, the nonwoven fabric excludes flameretardants other than the organophosphate ester. For example, thenonwoven fabric can exclude brominated polycarbonate. In someembodiments, the organophosphate ester is halogen-free. In someembodiments, the organophosphate ester comprises an oligomeric phosphateester, which can be a halogen-free oligomeric phosphate ester.

When the nonwoven fabric comprises the organophosphate ester flameretardant, it is present in an amount of 0.2 to 2 weight percent, basedon the weight of the nonwoven fabric. Within this range, the amount ofthe organophosphate ester flame retardant can be 0.3 to 1 weightpercent, or 0.4 to 0.9 weight percent.

The nonwoven fabric can, optionally, further comprise one or moreadditives known in the thermoplastics art. Suitable additives include,for example, stabilizers, mold release agents, lubricants, processingaids, drip retardants, nucleating agents, UV blockers, dyes, pigments,antioxidants, anti-static agents, blowing agents, mineral oil, metaldeactivators, antiblocking agents, and combinations thereof. Whenpresent, such additives are typically used in a total amount of lessthan or equal to 1 weight percent, based on the weight of the nonwovenfabric. In some embodiments, additives are used in an amount of lessthan or equal to 0.5 weight percent, or less than or equal to 0.2 weightpercent.

In some embodiments of the nonwoven fabric, the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 70 to 90 mole percent of the resorcinol esterunits, 5 to 15 mole percent of carbonate units wherein R¹ is1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weightpercent dimethylsiloxane units; and wherein the nonwoven fabric furthercomprises 0.2 to 2 weight percent of an organophosphate ester flameretardant.

In a very specific embodiment of the nonwoven fabric, it comprises,based on the weight of the nonwoven fabric, 30 to 50 weight percent ofthe reinforcing fibers, 40 to 60 weight percent of the polyimide, and 5to 15 weight percent of the block polyestercarbonate-polysiloxane, andfurther comprises, based on the weight of the nonwoven fabric, 0.3 to 3weight percent of a flame retardant; the reinforcing fibers compriseglass fibers; the polyimide comprises a polyetherimide; the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units in the block polyestercarbonate-polysiloxane,70 to 90 mole percent of the resorcinol ester units, 5 to 15 molepercent of carbonate units wherein R¹ is 1,3-phenylene, and 5 to 15 molepercent of carbonate units wherein R¹ is 2,2-bis(1,4-phenylene)propane,and further comprises, based on the weight of the blockpolyestercarbonate-polysiloxane, 0.3 to 3 weight percentdimethylsiloxane units; and the flame retardant comprises an oligomericphosphate ester.

The nonwoven fabric has a density of 0.03 to 0.2 gram/centimeter³.Density can be determined at 23° C. according to ASTM D792-13. Withinthe range of 0.03 to 0.2 gram/centimeter³, the density can be 0.033 to0.17 gram/centimeter³.

The nonwoven fabric has an areal density of 100 to 400 gram/meter².Areal density can be determined at 23° C. by weighing a 1.000 meter²section of fabric. Within the range of 100 to 400 gram/meter², the arealdensity can be 100 to 300 gram/meter².

The nonwoven fabric has a tensile modulus of 50 to 1000 megapascals,determined according to ASTM D638-14 at a temperature of 23° C. andusing a test speed of 50 millimeters/minute. Within the range of 50 to1000 megapascals, the tensile modulus can be 150 to 600 megapascals.

One embodiment is a method of forming a nonwoven fabric, the methodcomprising: forming an aqueous suspension layer comprising water, 25 to55 weight percent of reinforcing fibers, 35 to 65 weight percent ofpolyimide fibers, and 5 to 20 weight percent of binder fibers comprisinga block polyestercarbonate-polysiloxane, wherein weight percent valuesare based on the total weight of reinforcing fibers, polyimide fibers,and binder fibers; at least partially removing water from the aqueoussuspension layer to form a fiber layer; and exposing the fiber layer toa temperature of 250 to 320° C., thereby melting the binder fibers, atleast partially melting the polyimide fibers, and forming a nonwovenfabric; wherein the block polyestercarbonate-polysiloxane comprises apolyester block comprising resorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R¹ groups arearomatic divalent groups, and a polysiloxane block comprisingdimethylsiloxane units; wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5to 35 mole percent of carbonate units wherein R¹ is 1,3-phenylene, and 5to 35 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weightpercent dimethylsiloxane units.

The method comprises forming an aqueous suspension layer comprisingwater, reinforcing fibers, polyimide fibers, and binder fibers. Theaqueous suspension layer can be formed by depositing an aqueoussuspension of fibers onto a screen that retains the fibers.

The aqueous suspension layer comprises water, which is the residualwater after at least partially draining the liquid portion of theaqueous suspension through the screen. The water content of the aqueoussuspension layer is typically 1 to 25 weight percent, based on theweight of the aqueous suspension layer, and depending on the degree ofdrainage.

The aqueous suspension layer further comprises reinforcing fibers. Thereinforcing fibers are the same as those described above in the contextof the nonwoven fabric. The aqueous suspension layer comprises thereinforcing fibers in an amount of 25 to 55 weight percent, based on thetotal weight of reinforcing fibers, polyimide fibers, and binder fibers.Within this range, the amount of reinforcing fibers can be 30 to 50weight percent.

The aqueous suspension layer further comprises polyimide fibers. Theterm “polyimide fibers” refers to fibers containing 95 to 100 weightpercent polyimide, based on the weight of the polyimide fibers. When thepolyimide content is less than 100 weight percent, the balance istypically an additive that facilitates production or handling of thepolyimide fibers, such as, for example, a spin finish on the surface ofthe polyimide fibers. The polyimide of the polyimide fibers is the sameas the polyimide described above in the context of the nonwoven article.Methods of forming polyimide fibers are described, for example, in U.S.Pat. No. 4,994,544 to Nagahiro et al., and U.S. Pat. No. 5,716,567 toMusina et al. Polyimide fibers are also commercially available as, forexample, KURAKISSS™ polyimide fibers from Kuraray.

The aqueous suspension layer comprises the polyimide fibers in an amountof 35 to 65 weight percent, based on the total weight of reinforcingfibers, polyimide fibers, and binder fibers. Within this range, thepolyimide fiber amount can be 40 to 60 weight percent.

The aqueous suspension layer further comprises binder fibers comprisinga block polyestercarbonate-polysiloxane. The blockpolyestercarbonate-polysiloxane is the same as that described in thecontext of the nonwoven fabric. In some embodiments, the binder fiberscomprise 90 to 100 weight percent of the blockpolyestercarbonate-polysiloxane, based on the weight of the binderfibers.

In a very specific embodiment, the block polyestercarbonate-polysiloxanecomprises, based on total moles of carbonate and ester units in theblock polyestercarbonate-polysiloxane, 70 to 90 mole percent of theresorcinol ester units, 5 to 15 mole percent of carbonate units whereinR¹ is 1,3-phenylene, and 5 to 15 mole percent of carbonate units whereinR¹ is 2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weightpercent dimethylsiloxane units; the binder fibers further comprise anoligomeric aromatic phosphate ester; and the binder fibers comprise,based on the weight of the binder fibers, 90 to 98 weight percent of theblock polyestercarbonate-polysiloxane, and 2 to 10 weight percent of theoligomeric aromatic phosphate ester.

The aqueous suspension layer comprises the binder fibers in an amount of5 to 20 weight percent, based on the total weight of reinforcing fibers,polyimide fibers, and binder fibers. Within this range, the binder fiberamount can be 5 to 15 weight percent.

After the aqueous suspension layer is formed, the method comprises atleast partially removing water from the aqueous suspension layer to forma fiber layer. Water can be removed by methods including gravitydrainage through a screen on which the aqueous suspension layer can beformed, and passing the aqueous suspension layer through one or moresets of nip rollers.

After water is at least partially removed from the aqueous suspensionlayer, the method comprises exposing the fiber layer to a temperature of250 to 400° C., thereby melting the binder fibers, at least partiallymelting the polyimide fibers, and forming a nonwoven fabric. Thetemperature range of 250 to 400° C. is effective to melt the binderfibers and at least partially melt the polyimide fibers. Within thisrange, the temperature can be 260 to 350° C., or 270-320° C.

In some embodiments, the exposing the unconsolidated fiber layer to atemperature of 250 to 400° C. is conducted at a pressure of 40 to 400kilopascals. Within this range, the pressure can be 50 to 200kilopascals.

In some embodiments, the aqueous suspension layer and the fiber layerfurther comprise a viscosity modifying agent, and the method furthercomprises washing the fiber layer to at least partially remove theviscosity modifying agent.

In a very specific embodiment of the method, the aqueous suspensionlayer comprises 30 to 50 weight percent of the reinforcing fibers, 40 to60 weight percent of the polyimide fibers, and 5 to 15 weight percent ofthe binder fibers; the aqueous suspension layer and the fiber layerfurther comprise a viscosity modifying agent; the method furthercomprises washing the fiber layer to at least partially remove theviscosity modifying agent; the reinforcing fibers comprise glass fibers;the polyimide fibers comprise a polyetherimide; the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units in the block polyestercarbonate-polysiloxane,70 to 90 mole percent of the resorcinol ester units, 5 to 15 molepercent of carbonate units wherein R¹ is 1,3-phenylene, and 5 to 15 molepercent of carbonate units wherein R¹ is 2,2-bis(1,4-phenylene)propane,and further comprises, based on the weight of the blockpolyestercarbonate-polysiloxane, 0.3 to 3 weight percentdimethylsiloxane units; the binder fibers further comprise an oligomericaromatic phosphate ester; the binder fibers comprise, based on theweight of the binder fibers, 90 to 98 weight percent of the blockpolyestercarbonate-polysiloxane, and 2 to 10 weight percent of theoligomeric aromatic phosphate ester; and the exposing the unconsolidatedfiber layer to a temperature of 250 to 400° C. is conducted at apressure of 40 to 400 kilopascals.

Another embodiment is a composite, comprising, based on the weight ofthe composite: 25 to 55 weight percent of reinforcing fibers, 35 to 65weight percent of a polyimide, and 5 to 20 weight percent of a blockpolyestercarbonate-polysiloxane; wherein the blockpolyestercarbonate-polysiloxane comprises a polyester block comprisingresorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R¹ groups arearomatic divalent groups, and a polysiloxane block comprisingdimethylsiloxane units; wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5to 35 mole percent of carbonate units wherein R¹ is 1,3-phenylene, and 5to 35 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weightpercent dimethylsiloxane units; and wherein the composite has a densityof 0.92 to 1.38 gram/centimeter³, and an areal density of 100 to 3000gram/meter².

In some embodiments, the composite is prepared from multiple layers ofthe nonwoven fabric, with or without at least one scrim layer. Theoptional additional one or more scrim layer can include, for example, awoven glass scrim.

The composite comprises 25 to 55 weight percent of reinforcing fibers,based on the weight of the composite. Within this range, the amount ofreinforcing fibers can be 30 to 50 weight percent. The reinforcingfibers are the same as those described in the context of the nonwovenfabric.

The composite further comprises 35 to 65 weight percent of a polyimide,based on the weight of the composite. Within this range, the amount ofthe polyimide can be 40 to 60 weight percent. The polyimide is the sameas that described in the context of the nonwoven fabric.

The composite further comprises 5 to 20 weight percent of a blockpolyestercarbonate-polysiloxane, based on the weight of the composite.Within this range, the amount of block polyestercarbonate-polysiloxanecan be 5 to 15 weight percent. The block polyestercarbonate-polysiloxaneis the same as that described in the context of the nonwoven fabric.

In some embodiments of the composite, the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 70 to 90 mole percent of the resorcinol esterunits, 5 to 15 mole percent of carbonate units wherein R¹ is1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weightpercent dimethylsiloxane units; and the composite further comprises 0.2to 2 weight percent of an oligomeric aromatic phosphate ester flameretardant.

The composite has a density of 0.8 to 1.5 gram/centimeter³. Density canbe determined at 23° C. according to ASTM D792-13. Within the range of0.8 to 1.5 gram/centimeter³, the density can be 0.9 to 1.4gram/centimeter³, or 0.92 to 1.38 gram/centimeter³.

The composite has an areal density of 100 to 3000 gram/meter². Arealdensity can be determined at 23° C. by weighing a 1.000 meter² sectionof fabric. Within the range of 100 to 3000 gram/meter², the arealdensity can be 200 to 2500 gram/meter², or 300 to 2200 gram/meter².

In a very specific embodiment of the composite, the composite comprises,based on the weight of the composite, 30 to 50 weight percent of thereinforcing fibers, and 40 to 60 weight percent of the polyimide, and 5to 15 weight percent of the block polyestercarbonate-polysiloxane; thenonwoven fabric further comprises, based on the total weight of thenonwoven fabric, 0.3 to 3 weight percent of a flame retardant; whereinthe reinforcing fibers comprise glass fibers; wherein the polyimidecomprises a polyetherimide; the block polyestercarbonate-polysiloxanecomprises, based on total moles of carbonate and ester units in theblock polyestercarbonate-polysiloxane, 70 to 90 mole percent of theresorcinol ester units, 5 to 15 mole percent of carbonate units whereinR¹ is 1,3-phenylene, and 5 to 15 mole percent of carbonate units whereinR¹ is 2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weightpercent dimethylsiloxane units; and the flame retardant comprises anoligomeric aromatic phosphate ester.

Another embodiment is a method of forming a multilayer composite, themethod comprising: exposing at least two layers of the nonwoven fabricin any of its above-described variations to a temperature of 250 to 400°C. and a pressure of 300 to 1,500 kilopascals for a time of 60 to 600seconds to yield a multilayer composite.

Within the range of 250 to 400° C., the temperature can be 350 to 400°C.

Within the range of 300 to 1,500 kilopascals, the pressure can be 400 to1,200 kilopascals, or 500 to 1000 kilopascals.

Within the range of 60 to 600 seconds, the time can be 80 to 300seconds.

The invention includes at least the following embodiments.

Embodiment 1

A nonwoven fabric, comprising, based on the weight of the nonwovenfabric: 25 to 55 weight percent of reinforcing fibers, 35 to 65 weightpercent of a polyimide, and 5 to 20 weight percent of a blockpolyestercarbonate-polysiloxane; wherein the blockpolyestercarbonate-polysiloxane comprises a polyester block comprisingresorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R¹ groups arearomatic divalent groups, and a polysiloxane block comprisingdimethylsiloxane units; wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5to 35 mole percent of carbonate units wherein R¹ is 1,3-phenylene, and 5to 35 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weightpercent dimethylsiloxane units; wherein the nonwoven fabric has adensity of 0.03 to 0.2 gram/centimeter³, and an areal density of 100 to400 gram/meter²; and wherein the nonwoven fabric has a tensile modulusof 50 to 1000 megapascals, determined according to ASTM D638-14 at atemperature of 23° C. and using a test speed of 50 millimeters/minute.

Embodiment 2

The nonwoven fabric of embodiment 1, wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 70 to 90 mole percent of the resorcinol esterunits, 5 to 15 mole percent of carbonate units wherein R¹ is1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weightpercent dimethylsiloxane units; and wherein the nonwoven fabric furthercomprises 0.2 to 2 weight percent of an organophosphate ester flameretardant.

Embodiment 3

The nonwoven fabric of embodiment 2, wherein the organophosphate esterflame retardant comprises an oligomeric phosphate ester.

Embodiment 4

The nonwoven fabric of any one of embodiments 1-3, wherein thereinforcing fibers comprise glass fibers.

Embodiment 5

The nonwoven fabric of embodiment 1, wherein the nonwoven fabriccomprises, based on the weight of the nonwoven fabric, 30 to 50 weightpercent of the reinforcing fibers, 40 to 60 weight percent of thepolyimide, and 5 to 15 weight percent of the blockpolyestercarbonate-polysiloxane; wherein the nonwoven fabric furthercomprises, based on the weight of the nonwoven fabric, 0.3 to 3 weightpercent of a flame retardant; wherein the reinforcing fibers compriseglass fibers; wherein the polyimide comprises a polyetherimide; whereinthe block polyestercarbonate-polysiloxane comprises, based on totalmoles of carbonate and ester units in the blockpolyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinolester units, 5 to 15 mole percent of carbonate units wherein R¹ is1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weightpercent dimethylsiloxane units; and wherein the flame retardantcomprises an oligomeric phosphate ester.

Embodiment 6

A method of forming a nonwoven fabric, the method comprising: forming anaqueous suspension layer comprising water, 25 to 55 weight percent ofreinforcing fibers, 35 to 65 weight percent of polyimide fibers, and 5to 20 weight percent of binder fibers comprising a blockpolyestercarbonate-polysiloxane, wherein weight percent values are basedon the total weight of reinforcing fibers, polyimide fibers, and binderfibers; at least partially removing water from the aqueous suspensionlayer to form a fiber layer; and exposing the fiber layer to atemperature of 250 to 320° C., thereby melting the binder fibers, atleast partially melting the polyimide fibers, and forming a nonwovenfabric; wherein the block polyestercarbonate-polysiloxane comprises apolyester block comprising resorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R¹ groups arearomatic divalent groups, and a polysiloxane block comprisingdimethylsiloxane units; wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5to 35 mole percent of carbonate units wherein R¹ is 1,3-phenylene, and 5to 35 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weightpercent dimethylsiloxane units.

Embodiment 7

The method of embodiment 6, wherein the exposing the unconsolidatedfiber layer to a temperature of 250 to 400° C. is conducted at apressure of 40 to 400 kilopascals.

Embodiment 8

The method of embodiment 6 or 7, wherein the aqueous suspension layerand the fiber layer further comprise a viscosity modifying agent; andwherein the method further comprises washing the fiber layer to at leastpartially remove the viscosity modifying agent.

Embodiment 9

The method of any one of embodiments 6-8, wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units in the block polyestercarbonate-polysiloxane,70 to 90 mole percent of the resorcinol ester units, 5 to 15 molepercent of carbonate units wherein R¹ is 1,3-phenylene, and 5 to 15 molepercent of carbonate units wherein R¹ is 2,2-bis(1,4-phenylene)propane,and further comprises, based on the weight of the blockpolyestercarbonate-polysiloxane, 0.3 to 3 weight percentdimethylsiloxane units; wherein the binder fibers further comprise anoligomeric aromatic phosphate ester; and wherein the binder fiberscomprise, based on the weight of the binder fibers, 90 to 98 weightpercent of the block polyestercarbonate-polysiloxane, and 2 to 10 weightpercent of the oligomeric aromatic phosphate ester.

Embodiment 10

The method of embodiment 6, wherein the aqueous suspension layercomprises 30 to 50 weight percent of the reinforcing fibers, 40 to 60weight percent of the polyimide fibers, and 5 to 15 weight percent ofthe binder fibers; wherein the aqueous suspension layer and the fiberlayer further comprise a viscosity modifying agent; wherein the methodfurther comprises washing the fiber layer to at least partially removethe viscosity modifying agent; wherein the reinforcing fibers compriseglass fibers; wherein the polyimide fibers comprise a polyetherimide;wherein the block polyestercarbonate-polysiloxane comprises, based ontotal moles of carbonate and ester units in the blockpolyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinolester units, 5 to 15 mole percent of carbonate units wherein R¹ is1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weightpercent dimethylsiloxane units; wherein the binder fibers furthercomprise an oligomeric aromatic phosphate ester; wherein the binderfibers comprise, based on the weight of the binder fibers, 90 to 98weight percent of the block polyestercarbonate-polysiloxane, and 2 to 10weight percent of the oligomeric aromatic phosphate ester; and whereinthe exposing the unconsolidated fiber layer to a temperature of 250 to400° C. is conducted at a pressure of 40 to 400 kilopascals.

Embodiment 11

A composite, comprising, based on the weight of the composite: 25 to 55weight percent of reinforcing fibers, 35 to 65 weight percent of apolyimide, and 5 to 20 weight percent of a blockpolyestercarbonate-polysiloxane; wherein the blockpolyestercarbonate-polysiloxane comprises a polyester block comprisingresorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R¹ groups arearomatic divalent groups, and a polysiloxane block comprisingdimethylsiloxane units; wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5to 35 mole percent of carbonate units wherein R¹ is 1,3-phenylene, and 5to 35 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weightpercent dimethylsiloxane units; and wherein the composite has a densityof 0.92 to 1.38 gram/centimeter³, and an areal density of 100 to 3000gram/meter².

Embodiment 12

The composite of embodiment 11, wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 70 to 90 mole percent of the resorcinol esterunits, 5 to 15 mole percent of carbonate units wherein R¹ is1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weightpercent dimethylsiloxane units; and wherein the composite furthercomprises 0.2 to 2 weight percent of an oligomeric aromatic phosphateester flame retardant.

Embodiment 13

The composite of embodiment 11, wherein the composite comprises, basedon the weight of the composite, 30 to 50 weight percent of thereinforcing fibers, and 40 to 60 weight percent of the polyimide, and 5to 15 weight percent of the block polyestercarbonate-polysiloxane;wherein the nonwoven fabric further comprises, based on the total weightof the nonwoven fabric, 0.3 to 3 weight percent of a flame retardant;wherein the reinforcing fibers comprise glass fibers; wherein thepolyimide comprises a polyetherimide; wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units in the block polyestercarbonate-polysiloxane,70 to 90 mole percent of the resorcinol ester units, 5 to 15 molepercent of carbonate units wherein R¹ is 1,3-phenylene, and 5 to 15 molepercent of carbonate units wherein R¹ is 2,2-bis(1,4-phenylene)propane,and further comprises, based on the weight of the blockpolyestercarbonate-polysiloxane, 0.3 to 3 weight percentdimethylsiloxane units; and wherein the flame retardant comprises anoligomeric aromatic phosphate ester.

Embodiment 14

A method of forming a multilayer composite, the method comprising:exposing at least two layers of the nonwoven fabric of any one ofembodiments 1-5 to a temperature of 250 to 400° C. and a pressure of 300to 1,500 kilopascals for a time of 60 to 600 seconds to yield amultilayer composite.

All ranges disclosed herein are inclusive of the endpoints, and theendpoints are independently combinable with each other. Each rangedisclosed herein constitutes a disclosure of any point or sub-rangelying within the disclosed range.

The invention is further illustrated by the following non-limitingexamples.

Examples

Materials used in these examples are summarized in Table 1.

TABLE 1 Component Description GF Glass fibers, having a diameter ofabout 16 micrometers, and a length of about 12 millimeters; obtained asOPTIFLOW ™ 790C from Owens Corning. PEIF Polyetherimide fibers, 8 denierper filament with a fiber length of about 12 millimeters; obtained asKURAKISSS ™ UP801 8.8 dtex × 12 mm from Kuraray. PEC-Si para-Cumylphenolendcapped block polyestercarbonate- polysiloxane with about 99 weightpercent total of polyester blocks and polycarbonate blocks, and about 1weight percent polysiloxane blocks; the polyestercarbonate portioncontains about 80 mole percent 1,3-phenyleneisophthalate-co-terephthalate units, about 9 mole percent resorcinolcarbonate units, and about 11 mole percent bisphenol A carbonate units;the polysiloxane blocks have, on average, about 10 dimethylsiloxaneunits per block; the polyestercarbonate- polysiloxane has a weightaverage molecular weight of about 24,500 grams/mole and is preparable bythe procedure of Example 2-14 of Method 2 as described in U.S. Pat. No.7,790,292 B2 to Colburn et al., except that the p-cumylphenol level wasadjusted to achieve a weight average molecular weight of about 24,500grams/mole. OPE Oligomeric phosphate ester flame retardant; obtained inpowder form as FYROLFLEX ™ SOL-DP flame retardant from ICL IndustrialProducts. TBPDP Tetrakis(2,4-di-tert-butylphenyl)4,4′-biphenyldiphosphonite, CAS Reg. No. 119345-01-6; obtained as IRGAFOS ™P-EPQ from BASF.

The composition used to prepare block polyestercarbonate-polysiloxanecontaining fibers (PEC-Si fibers) is summarized in Table 2, wherecomponent amounts are expressed in weight percent based on the totalweight of the composition. The composition was prepared by dry blendingall components and adding the resulting mixture to the feed throat of atwin-screw extruder operating with zone temperatures ranging from 230 to300° C. The extrudate was cooled in water before being pelletized.

TABLE 2 Component Amount PEC-Si 93.44 OPE 6.50 TBPDP 0.06

Pellets were dried at 80 to 120° C. for 6 to 12 hours before being fedto the hopper of a melt spinning apparatus. The melt spinning apparatusis schematically illustrated in FIG. 1, where melt spinning apparatus 1comprises extruder 5, in which dried pellets are converted to a melt,melt pump 10, which conveys the melt to spin pack 15, where it isfiltered, then to spinneret 20, where multiple fibers are formed fromthe filtered melt. The fibers are immediately conveyed to quench section30, where they are air-cooled and solidified. The cooled fibers thenenter spin finish section 40, where a spin finish can be applied to thesurface of the fibers. The fibers then traverse a sequence of godetpairs comprising first godets 50, second godets 60, and third godets 70,where the fibers are drawn (stretched). The fibers then enter windersection 80, where contact roller 90 facilitates formation of wound fiber100 around one of two winding cores 110.

In these experiments, the melt pump was operated at 10centimeter³/revolution. Extruder and melt pump temperatures were 280 to330° C. A 144-hole, single-position spinneret was used. Spinneret holes(nozzles) were circular with a diameter of 0.8 millimeters. Thelength-to-diameter ratio of each spinneret was 4:1. A 325 U.S. mesh (44micrometer opening) screen filter was used in the spinpack forfiltration of the composition melt. After fibers exited the nozzles,they were solidified by quenching with air at ambient temperature (about23° C.). Individual filaments were combined to form multi-filamentthreads, then a spin finish (an acrylamide copolymer in an oil-in-wateremulsion, obtained as LUROL™ PS-11744 from Goulston) was applied to themulti-filament threads before they contacted the first godet. The drawdown ratio was 280 to 550. Draw down ratio, which is unitless, isdefined as the ratio of speed (in meters/minute) at which the melt exitsthe spinneret nozzles to the speed (in meters/minute) of the fiber atthe first godet. The apparent shear rate was 170 to 1700 second⁻¹.Apparent shear rate (in units of second⁻¹) is defined according to theequation

Apparent shear rate (second⁻¹)=4Q/πR³ρ

wherein Q is the melt throughput per spinneret nozzle (in grams/second),R is the nozzle radius (in centimeters), and ρ is the polymer meltdensity (in grams/centimeter³). The mechanical draw ratio was 0.95 to1.2. Mechanical draw ratio, which is unitless, is defined as the ratioof the first godet speed (in meters/minute) to the winder speed (inmeters/minute). The resulting threads, containing fibers of 8 denier perfilament, were chopped to a length of about 12 millimeters for use inpreparation of a nonwoven fabric.

Formation of Nonwoven Fabric. A mixture of polyetherimide fibers (50weight percent), PEC-Si fibers (10 weight percent), and chopped glassfibers (40 weight percent) was used to prepare a nonwoven fabric via awet-laid papermaking) process. FIG. 2 is a schematic illustration of apapermaking apparatus 200, which includes mixing tank 210, run tank 220,headbox 230, wire former 240, dryer 250, and winder 260. A fiberdispersion was prepared by dispersing 200 kilograms total of the threeingredient fibers in 200 kilograms of an aqueous solution containing aviscosity modifying agent. The viscosity modifying agent was apoly(acrylamide-co-diallyldimethylammonium chloride) solution, 10 weightpercent in water, and it was used in an amount effective to provide theaqueous solution with a viscosity of 50 to 200 centipoise. The fiberdispersion was fed onto the wire mesh of a paper-making machine to forman aqueous suspension layer, and aqueous solution was drained to form afiber layer. The fiber layer was transferred to a water washing sectionwhere viscosity modifier was washed from the fiber layer. The washedfiber layer was then transferred to a tunnel dryer, and finally to awinding section. Water was essentially eliminated from the mat by thesequence of gravity drainage through holes in the wire mesh, squeezingthrough several pairs of nip rollers, and heating in an ambient-pressuretunnel dryer, where the temperature was set to 280-300° C. and the drierresidence time was 120-180 seconds. In this temperature range, thePEC-Si fibers melted and the polyetherimide fibers at least partiallymelted. Both types of fibers flowed, losing their fiber shape. If thetunnel dryer temperature is less than 280° C., web tearing occurs. If itis less than 220° C., not only is there web tearing, but the binder(PEC-Si) fibers do not get fully activated, leading to a weak andlocally torn fabric. This stage is referred to as binder activation,because the binder fibers melt, and the melted PEC-Si copolymer flowswithin the web to bind together the network of glass and polyetherimidefibers. This gives the network enough mechanical integrity to prevent itfrom falling apart in subsequent processing and handling. Using theabove process steps, a 165 gram/meter² nonwoven fabric web was producedat a speed of 5 meters/minute. The nonwoven fabric web was wound on acore. When the roll was fully wound, the edges were trimmed to meet thetarget width, and the nonwoven fabric web was re-wound to a new core.

As a comparison, a 325 gram/meter² non-consolidated nonwoven fabric wasproduced from the same fiber mix (40% glass fiber, 50% polyetherimidefiber, and 10% PEC-Si fiber) and the same process, except that the fiberdispersion did not include a viscosity modifier, there was no waterwashing step, and the dryer temperature was 200° C.

Tensile properties for the 165 gram/meter² nonwoven fabric and the 325gram/meter² non-consolidated nonwoven fabric were determined accordingto ASTM D638-14 at 23° C. using a test speed of 50 millimeters/second.The 165 gram/meter² nonwoven fabric exhibited a tensile modulus of 293megapascals, and a tensile strain at break of 1.6 percent. The 325gram/meter² non-consolidated nonwoven fabric exhibited a tensile modulusof 16 megapascals, and a tensile strain at break of 4.5 percent.

FIG. 3 provides images of rolls of (a) 325 gram/meter² non-consolidatednonwoven fabric, and (b) 165 gram/meter² nonwoven fabric. Note that thestiffer pre-consolidated nonwoven fabric assumes an essentially planarshape when unwound from the roll, while the less stiff non-consolidatednonwoven fabric hangs limply. The greater stiffness of thepre-consolidated nonwoven fabric provides advantages including ease oftrimming, ease of shearing into complex shapes, shape retention withoutunderlying support.

Additional advantages of the pre-consolidated nonwoven fabric relativeto the non-consolidated nonwoven fabric are that it surrounds thereinforcing fibers with more resin, and that it has smoother and moreuniform surfaces. Both of these advantages contribute to less fibershedding during nonwoven fabric handling. FIG. 4 provides opticalmicrographs of (a) 325 gram/meter² non-consolidated nonwoven fabric, and(b) 165 gram/meter² pre-consolidated nonwoven fabric. These micrographsshow that the pre-consolidated nonwoven fabric surrounds the reinforcingfibers with more resin than the non-consolidated nonwoven fabric. FIG. 5provides surface profiles, derived from optical micrographs, of (a) 325gram/meter² non-consolidated nonwoven nonwoven fabric, and (b) 165gram/meter² nonwoven fabric. These surface profiles show that thepre-consolidated nonwoven fabric has smoother and more uniform surfacesthan the non-consolidated nonwoven fabric.

The nonwoven fabric was used to form a consolidated multi-layercomposite suitable for thermoforming. Seven or eight layers of the 165gram/meter² pre-consolidated nonwoven fabric were unwound fromindependently operating pay-off winders, stacked one over another, thentopped with one layer of 10-20 gram/meter² glass fiber woven fabricscrim obtained as BGF 104 from BGF Industries (Greensboro, N.C., USA).The combined layers were then passed through a consolidation apparatus.The consolidation apparatus was a steel double belt press obtained asHeather 5 from HELD Technologie GmbH (Trossingen, Germany). The nonwovenweb was exposed to radiation from an infrared pre-heating device beforeit was fed to the double-belt press. The double-belt press consolidationsimultaneously compressed the nonwoven fabrics and caused thepolyetherimide fibers to melt and flow. A mold release agent, LOCTITE™FREKOTE™ 700-NC from Henkel, was continuously applied to the steel beltsto prevent sticking of the nonwoven webs to the steel belts. Typicalconsolidation conditions were 180 to 300 seconds at a temperature of 350to 400° C., and a pressure of 800 kilopascals. Consolidation wasfollowed by cooling while maintaining pressure. The cooled, consolidatedcomposite had a continuous resin matrix containing strained glassfibers. The strained glass fibers release their residual stress andcreate “lofting” during a subsequent thermoforming process. The mass perunit area of the consolidated mat was 1,155 grams/meter² for theseven-layer composite, and 1,320 grams/meter² for the eight-layercomposite. The thickness of the consolidated composite was 1.05millimeters for a seven-layer composite, and 1.20 millimeters for theeight-layer composite. The width of the consolidated panel is variableand can be controlled, for example, using an in-line edge trimmer. Thelength of the consolidated panel is variable and can be controlled, forexample, using a guillotine cutter on the consolidation apparatus.

1. A nonwoven fabric, comprising, based on the weight of the nonwovenfabric: 25 to 55 weight percent of reinforcing fibers, 35 to 65 weightpercent of a polyimide, and 5 to 20 weight percent of a blockpolyestercarbonate-polysiloxane; wherein the blockpolyestercarbonate-polysiloxane comprises a polyester block comprisingresorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R¹ groups arearomatic divalent groups, and a polysiloxane block comprisingdimethylsiloxane units; wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5to 35 mole percent of carbonate units wherein R¹ is 1,3-phenylene, and 5to 35 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weightpercent dimethylsiloxane units; wherein the nonwoven fabric has adensity of 0.03 to 0.2 gram/centimeter³, and an areal density of 100 to400 gram/meter²; and wherein the nonwoven fabric has a tensile modulusof 50 to 1000 megapascals, determined according to ASTM D638-14 at atemperature of 23° C. and using a test speed of 50 millimeters/minute.2. The nonwoven fabric of claim 1, wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 70 to 90 mole percent of the resorcinol esterunits, 5 to 15 mole percent of carbonate units wherein R¹ is1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weightpercent dimethylsiloxane units; and wherein the nonwoven fabric furthercomprises 0.2 to 2 weight percent of an organophosphate ester flameretardant.
 3. The nonwoven fabric of claim 2, wherein theorganophosphate ester flame retardant comprises an oligomeric phosphateester.
 4. The nonwoven fabric of claim 1, wherein the reinforcing fiberscomprise glass fibers.
 5. The nonwoven fabric of claim 1, wherein thenonwoven fabric comprises, based on the weight of the nonwoven fabric,30 to 50 weight percent of the reinforcing fibers, 40 to 60 weightpercent of the polyimide, and 5 to 15 weight percent of the blockpolyestercarbonate-polysiloxane; wherein the nonwoven fabric furthercomprises, based on the weight of the nonwoven fabric, 0.3 to 3 weightpercent of a flame retardant; wherein the reinforcing fibers compriseglass fibers; wherein the polyimide comprises a polyetherimide; whereinthe block polyestercarbonate-polysiloxane comprises, based on totalmoles of carbonate and ester units in the blockpolyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinolester units, 5 to 15 mole percent of carbonate units wherein R¹ is1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weightpercent dimethylsiloxane units; and wherein the flame retardantcomprises an oligomeric phosphate ester.
 6. A method of forming anonwoven fabric, the method comprising: forming an aqueous suspensionlayer comprising water, 25 to 55 weight percent of reinforcing fibers,35 to 65 weight percent of polyimide fibers, and 5 to 20 weight percentof binder fibers comprising a block polyestercarbonate-polysiloxane,wherein weight percent values are based on the total weight ofreinforcing fibers, polyimide fibers, and binder fibers; at leastpartially removing water from the aqueous suspension layer to form afiber layer; and exposing the fiber layer to a temperature of 250 to320° C., thereby melting the binder fibers, at least partially meltingthe polyimide fibers, and forming a nonwoven fabric; wherein the blockpolyestercarbonate-polysiloxane comprises a polyester block comprisingresorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R¹ groups arearomatic divalent groups, and a polysiloxane block comprisingdimethylsiloxane units; wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5to 35 mole percent of carbonate units wherein R¹ is 1,3-phenylene, and 5to 35 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weightpercent dimethylsiloxane units.
 7. The method of claim 6, wherein theexposing the unconsolidated fiber layer to a temperature of 250 to 400°C. is conducted at a pressure of 40 to 400 kilopascals.
 8. The method ofclaim 6, wherein the aqueous suspension layer and the fiber layerfurther comprise a viscosity modifying agent; and wherein the methodfurther comprises washing the fiber layer to at least partially removethe viscosity modifying agent.
 9. The method of claim 6, wherein theblock polyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units in the block polyestercarbonate-polysiloxane,70 to 90 mole percent of the resorcinol ester units, 5 to 15 molepercent of carbonate units wherein R¹ is 1,3-phenylene, and 5 to 15 molepercent of carbonate units wherein R¹ is 2,2-bis(1,4-phenylene)propane,and further comprises, based on the weight of the blockpolyestercarbonate-polysiloxane, 0.3 to 3 weight percentdimethylsiloxane units; wherein the binder fibers further comprise anoligomeric aromatic phosphate ester; and wherein the binder fiberscomprise, based on the weight of the binder fibers, 90 to 98 weightpercent of the block polyestercarbonate-polysiloxane, and 2 to 10 weightpercent of the oligomeric aromatic phosphate ester.
 10. The method ofclaim 6, wherein the aqueous suspension layer comprises 30 to 50 weightpercent of the reinforcing fibers, 40 to 60 weight percent of thepolyimide fibers, and 5 to 15 weight percent of the binder fibers;wherein the aqueous suspension layer and the fiber layer furthercomprise a viscosity modifying agent; wherein the method furthercomprises washing the fiber layer to at least partially remove theviscosity modifying agent; wherein the reinforcing fibers comprise glassfibers; wherein the polyimide fibers comprise a polyetherimide; whereinthe block polyestercarbonate-polysiloxane comprises, based on totalmoles of carbonate and ester units in the blockpolyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinolester units, 5 to 15 mole percent of carbonate units wherein R¹ is1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weightpercent dimethylsiloxane units; wherein the binder fibers furthercomprise an oligomeric aromatic phosphate ester; wherein the binderfibers comprise, based on the weight of the binder fibers, 90 to 98weight percent of the block polyestercarbonate-polysiloxane, and 2 to 10weight percent of the oligomeric aromatic phosphate ester; and whereinthe exposing the unconsolidated fiber layer to a temperature of 250 to400° C. is conducted at a pressure of 40 to 400 kilopascals.
 11. Acomposite, comprising, based on the weight of the composite: 25 to 55weight percent of reinforcing fibers, 35 to 65 weight percent of apolyimide, and 5 to 20 weight percent of a blockpolyestercarbonate-polysiloxane; wherein the blockpolyestercarbonate-polysiloxane comprises a polyester block comprisingresorcinol ester units having the structure

a polycarbonate block comprising carbonate units having the structure

wherein at least 60 percent of the total number of R¹ groups arearomatic divalent groups, and a polysiloxane block comprisingdimethylsiloxane units; wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5to 35 mole percent of carbonate units wherein R¹ is 1,3-phenylene, and 5to 35 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weightpercent dimethylsiloxane units; and wherein the composite has a densityof 0.92 to 1.38 gram/centimeter³, and an areal density of 100 to 3000gram/meter².
 12. The composite of claim 11, wherein the blockpolyestercarbonate-polysiloxane comprises, based on total moles ofcarbonate and ester units, 70 to 90 mole percent of the resorcinol esterunits, 5 to 15 mole percent of carbonate units wherein R¹ is1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weightpercent dimethylsiloxane units; and wherein the composite furthercomprises 0.2 to 2 weight percent of an oligomeric aromatic phosphateester flame retardant.
 13. The composite of claim 11, wherein thecomposite comprises, based on the weight of the composite, 30 to 50weight percent of the reinforcing fibers, and 40 to 60 weight percent ofthe polyimide, and 5 to 15 weight percent of the blockpolyestercarbonate-polysiloxane; wherein the nonwoven fabric furthercomprises, based on the total weight of the nonwoven fabric, 0.3 to 3weight percent of a flame retardant; wherein the reinforcing fiberscomprise glass fibers; wherein the polyimide comprises a polyetherimide;wherein the block polyestercarbonate-polysiloxane comprises, based ontotal moles of carbonate and ester units in the blockpolyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinolester units, 5 to 15 mole percent of carbonate units wherein R¹ is1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R¹ is2,2-bis(1,4-phenylene)propane, and further comprises, based on theweight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weightpercent dimethylsiloxane units; and wherein the flame retardantcomprises an oligomeric aromatic phosphate ester.
 14. A method offorming a multilayer composite, the method comprising: exposing at leasttwo layers of the nonwoven fabric of claim 1 to a temperature of 250 to400° C. and a pressure of 300 to 1,500 kilopascals for a time of 60 to600 seconds to yield a multilayer composite.